I don’t know anything particular about the Marquee specifically, except it is a hybrid electrostatic-dynamic driver center channel speaker.
The speaker needs to be plugged in to power bias for the electrostatic panel.
The bias should be turned up as high as possible without causing any sparking type noise. It is easiest to adjust this without any music playing.
Brilliance is high frequency response adjustment.
Older models of SoundLabs are less efficient than newer models. Yes, it makes sense that the speaker plays quieter.